A hybrid vehicle conventionally is equipped with, for example, a high voltage power supply device and a low voltage power supply device. The high voltage power supply device is for supplying electric power to an electric motor or the like for driving a vehicle. The low voltage power supply device is for supplying electric power to an electronic control unit, an electric actuator or the like for controlling a vehicle. The low voltage power supply device is charged by lowering the high voltage of the high voltage power supply device by a DC-DC converter.
It is also conventional (for example, P-A-2012-115031) that a DC-DC converter is used to convert a high voltage of a high voltage power supply device or a low voltage of a low voltage power supply device to an intermediate voltage, which is between the high voltage and the low voltage, so that the intermediate voltage may also be used as a power supply voltage for a vehicle.
The high voltage, the intermediate voltage and the low voltage, which are power supply voltages for a vehicle, tend to vary with temperature, power consumption and the like. It is proposed to control a DC-DC converter and the like based on voltage variations of such voltages. Specifically, the high voltage is corrected based on a voltage variation amount of the high voltage, the intermediate voltage is corrected base on a voltage variation amount of the intermediate voltage and the low voltage is corrected based on a voltage variation amount of the low voltage.
However, since those voltages are related one another because of the voltage conversion operation by the DC-DC converter, it is difficult to set those voltages to respective target voltage values even if the voltages are corrected individually.